1. Field of the Invention
The invention relates to a device for the comminution of free-flowing feed material through which air flows.
2. Description of the Background Art
Such devices are associated with the field of mechanical process engineering and serve to comminute free-flowing substances such as, for example, minerals, pharmaceutical and chemical substances, foodstuffs, materials containing cellulose, synthetics, and the like. Typical for such devices is an air stream produced by a rotor, so-called internal air, which assumes the transportation of the feed material into and out of the comminution device and also ensures the cooling of the feed material and the comminution tools. In addition, subject to its flow speed, the internal air determines the length of stay of the feed material in the comminution section and thus the degree of comminution. The precise adherence to the machine-specific internal air quantity during operation of generic devices is thus highly important for producing a high-quality, final product.
To prevent damage of devices due to foreign particles in the feed material, it is further a known practice to provide a gravity sifter at the material infeed. By a significant change in material flow direction at the comminution device infeed, due to their mass inertia, foreign particles are separated from the material stream, wherein the separation limit is determined by the speed of the material stream. In order to adhere to a predetermined separation limit, it is thus necessary to supply the gravity sifter with a constant loading rate.
A problem which arises here is that as a rule, the internal air quantity of a comminution device is much greater than the internal air quantity of the upstream sifter. Operating a comminution device with an optimal internal air quantity leads to material stream speeds in the sieve passage in which undesirably, also useful feed material is discharged from the material stream.
In order to avoid this, a comminution machine through which gas flows is known from DE 43 16 350 C1, which corresponds to U.S. Pat. No. 5,529,250, and which is incorporated herein by reference, and which contains an upstream infeed apparatus with a sieve passage, wherein in the sieve passage a fan additionally feeds in air.